Morphologies of Galaxies in and around a Protocluster at Z = 2.300

We present results from the first robust investigation of galaxy morphology as a function of environment at z > 1.5. Our study is motivated by the fact that star-forming galaxies contained within a protocluster at z = 2.3 in the HS1700+64 field are characterized by significantly older ages and larger stellar masses on average than those at similar redshifts but more typical environmental densities. In the analysis of HST/ACS images, we apply non-parametric statistics to characterize the rest-frame UV morphologies of a sample of 85 UV-selected star-forming galaxies at z = 1.7 − 2.9, 22 of which are contained in the protocluster. The remaining 63 galaxies are not in the protocluster but have a similar mean redshift of z̄ ∼ 2.3, and constitute our control sample. We find no environmental dependence for the distributions of morphological properties. Combining the measured morphologies with the results of population synthesis modeling, we find only weak correlations, if any, between morphological properties and measures of stellar population such as stellar mass, age, extinction and star-formation rate. These findings are similar to results from other recent work. Given the incomplete census of the protocluster galaxy population, which is weighted towards star-forming galaxies, and the lack of correlation between rest-frame UV morphology and star-formation history at z ∼ 2 within our sample, the absence of environmental trends in the distribution of morphological properties is not surprising. We do, however, find some non-environmental trends with morphology. The degree of nebulosity and apparent rest-frame UV size appears to correlate with the UV-luminosity (uncorrected for dust extinction), which we demonstrate is not an artifact of finite signal-to-noise. Additionally, using a larger sample of photometric candidates, most of which do not have spectroscopic redshifts, we compare morphological distributions for 282 UV-selected and 43 near-IR-selected galaxies. While the observed difference in the degree of nebulosity between the two samples appears to be a byproduct of the fainter average rest-frame UV surface brightness of the near-IR-selected galaxies, we find that, among the lowest surface brightness galaxies, the near-IR-selected objects have significantly smaller angular sizes. Subject headings: galaxies: high redshift — galaxies: structure — galaxies: clusters — cosmology: